1. Field of the Invention
The present invention relates to a grease composition, and more particularly to a carbonate-based grease composition having such excellent characteristics that rotating torque is small, noise is small and life is long when the grease of the present invention is sealed in a bearing.
2. Description of the Related Art
Recently, earth environmental problem is particularly closed up, and an effort to reduce consumption of wasteful energy as less as possible is obligated to advanced countries. As one conclusion of energy saving problem, it is the current demand for using DC motor having good efficiency in place of AC motor. In particular, in fan motors of air conditioners for appliances, it has been approaching the age that DC motor having good efficiency is used in place of AC motor that has still the limitation even though a converter is provided to change an output.
In general, the performances required to a bearing grease composition used in a small-sized motor for use in appliances or the like are such that torque is small, acoustic performance is excellent, leakage (volatilization) is small and life is long.
A lithium soap-based grease using a mineral oil as a base oil, or a lithium soap-based grease using, as a base oil, a synthetic ester (diester oil, polyol ester oil or the like) that is a reaction product of an organic acid and an alcohol has conventionally been used as the bearing grease for motor, but it is the actual circumstances that further improvement is still required.
A lithium soap-based grease using a mineral oil as a base oil has been used as a general-purpose grease for many years, but has had the problems that for a small-sized motor, a thickening agent has poor dispersibility in a grease, acoustic and vibration properties at the rotation of bearing are not good, and temperature range of use is narrow.
Further, a lithium soap-based grease using, as a base oil, a synthetic ester (diester oil, polyol ester oil or the like) that is a reaction product of an organic acid and an alcohol has good dispersity of the lithium soap. Therefore, there is no problem on acoustic and vibration performances at the rotation of bearing, and the wide temperature range of use due to the use of a synthetic oil was preferable. However, this grease had the problem in low torque property that is the essential element inmotors for appliances in recent years.